This invention relates to charge transfer imaging to create latent images on a dielectric for subsequent toning and transfer to a carrier. More particularly, the invention includes cartridges for creating the images.
The present invention is described herein with reference to an exemplary printer which utilizes a dielectric coated print drum. However, it will be clear to those skilled in the art that the present invention may also be used in combination with printers utilizing different configurations of image receiving surfaces, and indeed may be useful in machines other than printers.
There is an increasing need for peripherals which can accept a computer or word processor output and convert the output to an image on paper, commonly called a "hard copy". Typically such a peripheral is a printer which uses a charge transfer process similar to that described in U.S. Pat. Ser. Nos. 4,155,093 to Fotland and Carrish, or 4,160,257 to Carrish, which utilizes a combination of electrodes about a dielectric which can be controlled to place a charge on a drum coated for instance with aluminum oxide impregnated with a wax. In this way a latent image is built up corresponding to the image to be produced on the paper, and the latent image is then toned and transferred to the paper and fused. Should it be necessary to produce a second copy, the procedure is repeated to give as many copies as necessary. Further, it is possible to vary the image by electronic control so that parts of the image can be printed, or the complete image can be turned through 90 degrees with respect to the paper. These possible variations make such printers desirable equipment wherever hard copies of electronically generated information are required.
The print cartridge is located adjacent the print drum surface and normally extends parallel to the axis of rotation of the drum. The inner or discharge surface of the cartridge, which faces the drum surface and includes the source of the charge, must be accurately spaced from the drum such that it is close enough to produce a clear image, and yet far enough away to prevent flashover between the electrodes of the cartridge and the drum.
An example of cartridge construction is described in applicant's U.S. Pat. Ser. No. 4,679,060 and allowed U.S. patent application Ser. No. 07/014,408, both to McCallum et al. This cartridge includes a number of relatively thin planar structural layers and produces a charge transfer image by means of a charge generator in the form of a matrix of electrodes located on an inner surface of the cartridge. Outer surfaces of the cartridge facing away from the drum are provided with contacts for electrical connection of individual electrodes with corresponding spring biased contacts linked to a cartridge control board, also known as a mother board, for controlling the image generation. An exemplary configuration of printer for receiving such a cartrige is described in applicant's U.S. patent Ser. No. 4,516,847 to Maczuszenko et al. The cartridge also includes an aluminum spine which rigidifies the cartridge and extends outwardly to provide a handle to be used when the cartridge is being fitted or removed from the printer.
The cartridge is mounted in a printer on mounting blocks which are adjusted relative to rigid parts of the print structure using shims to give the desired spacing between the cartridge and the drum surface (typically 0.01 inches). Understandably, it would be difficult to adjust this spacing each time a cartridge was replaced. Accordingly, the mounting blocks are set-up during assembly of the printer and are not normally adjusted during the life of the printer, so that replacement cartridges must be accurately located on the mounting blocks. To achieve this accurate location, the lower contact surface of each cartridge must be accurately sized and is, therefore, formed of a substantial piece of high grade material, typically high grade fibre glass reinforced epoxy, which adds considerably to the cost of the cartridge. Also, particles of dust or the like may find their way between the contact surfaces of the cartridge and mounting and thus affect the spacing.
Connections between the contacts on the outer face of the cartridge and the mother board are made by spring pin contacts which extend downwardly from the mother board. These contacts are relatively expensive and the total cost of the 260 or so contacts required for a cartridge adds significantly to the total cost of the printer. Also, the spring forces exterted on the cartridge contacts by the spring contacts further complicate the accurate location of the cartridge because the accumulation of the small forces tends to push the cartridge towards the drum, and could affect the spacing between the cartridge and drum.
Other forms of cartridges are available which provide the cartridge contacts on the inner face of the cartridge and do not require such expensive spring pin contacts. However, the mother board contacts for such cartridges must be located in the restricted space between the cartridge and the drum, the space becoming more restricted as larger diameter print drums are utilized. These cartridges also suffer from the disadvantage that the spring forces from the mother board contacts tend to push the cartridge away from the drum, and again could affect the spacing between the cartridge and the drum.
These disadvantages lead to the design of a different configuration of cartridge and cartridge mounting, as described in applicant's copending U.S. Patent Application entitled Charge Transfer Imaging Cartridge Mounting and Printer. The cartridge described therein includes a rectangular cross section spine, the inner portion of the cartridge being located on an inner face of the spine and the cartridge contacts being located on side faces of the spine. The cartridge is located in a channel defined by two spaced elements, from which spring biased mother board contacts extend to bear against the cartridge contacts. As the spring forces from the mother board contacts are acting on the cartridge parallel to the inner face and the drum surface, the forces do not tend to affect the spacing between the cartridge and the drum.
It is clear that conventional methods of cartridge construction, such as that described in U.S. Pat. Ser. No. 4,679,060 and allowed U.S. Patent application Ser. No. 07/014,408, would be unsuitable to produce a cartridge having the cartridge contacts which are inclined with respect to the plane of the discharge portion, because these methods are directed towards the production of rigid planar cartridges. Similarly, manufacturing a non-planar cartridge by conventional methods would be difficult as photoetching is used to produce many of the individual components of the cartridge and it would be very difficult to use this process on anything other than planar surfaces.